The role of catalase in resistance to boron toxicity after melatonin application (MEL) was investigated in Arabidopsis thaliana plants. Col-0 and cat2-2 plants were exposed to 50 μM MEL followed by boron toxicity (BT) in a medium containing 10 mM H ₃BO ₃. Pigment loss and accordingly chlorosis were reduced by melatonin under BT conditions, while they were more prominent in cat2-2 mutants. Moreover, TBARS and H ₂O ₂ contents, which increased due to BT, decreased as a result of melatonin application and the levels of these parameters in cat2-2 mutants were higher than the values in Col-0. Antioxidant enzyme activity of SOD and SOD1 gen transcript were induced by MEL under BT. Conversely, APX4, PER10 and CAT1 transcripts were down-regulated by MEL under BT. In addition, antioxidant enzyme activities and their transcript levels were lower than those of Col-0. Thus, we suggested that MEL scavenged ROS directly under BT. Melatonin also reduced the accumulation of boric acid in leaf tissues of Col-0, but not cat2-2. Finally, even though melatonin application provided a degree of endurance, the cat2 mutation resulted in increased sensitivity to BT.

Cucumber mosaic virus (CMV; family Bromoviridae, genus Cucumovirus) is the most cosmopolitan plant virus occurring worldwide. In the present study, leaf samples showing deformations, mosaics, and chlorotic spots symptoms were collected from naturally infected Basella alba, Telfairia occidentalis and Talinum fruticosum in a home yard garden in Ibadan, Nigeria. Total nucleic acid was extracted from leaves and used as template for cDNA synthesis. RT-PCR was carried out using CMV-specific primers targeting RNA-1 segment. Samples were also tested by RT-PCR using Potyvirus and Begomovirus genusspecific primers. DNA fragments with the expected sizes of ~500 bp were amplified by using CMV-specific primers; however, the expected amplicons were not produced using specific primers used for the detection of potyviruses and begomoviruses. The nucleotide and deduced amino acid sequences obtained for the isolates studied contained 503–511 nt and 144 aa, respectively. The isolates shared 81.9–85.3% nucleotide and 74.3–77.8% amino acid sequence identities with each other. The results of BLASTN analyses showed the highest identities of the isolates (80–93%) with CMV strains from Japan, USA and South Korea. Alignment of deduced partial protein revealed multiple amino acid substitutions within the three isolates and high identities with CMV subgroup I. Phylogenetic analyses putatively categorized the isolates in close association with subgroup IB isolates. The three isolates clustered together into a separate subclade, indicating possible new CMV strains. The results provide the first molecular evidence for CMV infections of T. fruticosum and B. alba in Nigeria and seem to show the possible presence of new strain(s). These findings also add three new hosts to the list of natural host range of the virus in Nigeria.